Relay driver for Raspberry Pi and other systems

Some people wish to interface this relay kit with 3.3V systems such as the Raspberry Pi, or systems which cannot support the 28mA relay current from processor I/O pins directly. This relay driver is suitable for such cases. Read more here...

Kit photos

The photos below show the relay-switched LPF board plugged into the back of the U3/U3S kit. Note that my photos below show NO additional LPF's plugged in (as I only had one built LPF at the time of those photos).

Using the Rev. 5 relay-switched LPF kit to switch Band Pass Filters

QRP Labs Band Pass Filter kits have the same pinout and footprint as the Low Pass Filter kits, so they also fit the relay-switched filter kit. Use Band Pass filter kits only for receiver input filtering (they should not be used at a transmitter output). In the standard configuration described in the assembly manual, the LPF kit inserted on the right (in position 1) is ALWAYS in-circuit and should be the filter for the highest frequency band installed. However, this is not suitable for when you wish to use the kit to switch band pass filters.

Note that the output SMA connector(s) on the right side of the board are connected permanently to the final (position 1) filter output. Therefore you cannot use them as the output, when using the board for Band Pass filter kit switching. In this case you should take the RF output from the connections circled in yellow, in the diagram. The RF input is the RFI pin of the 2 x 5-pin header on the left of the board (same as in the Low Pass Filter kit usage). An alternative is to cut the track from the SMA connector center pins and add a wire to connect it to the common bus track that runs horizontally across the board, finishing at the "RF" pad circled in yellow.

The relay-switched LPF kit can be used with a common RF output, which is the default connection described in the manual. However it can also allow the relays to switch between up to 6 different outputs. This could be used to select different antennas, for example. It could allow antenna comparison experiments, or the use of different antennas for matching different bands.

The jumper configuration below shows the kit used to select between 6 different outputs. The output of each LPF is routed to a different pad on the board. The outputs are labelled 0 to 5 in the diagram. Note that relay 0 is the one on the main Ultimate3/3S kit PCB (when the relay board is in use with the U3/U3S kits).